【作者】 王芳；

【导师】 刘玉芳；

【作者基本信息】 河南师范大学 ， 物理学、光学， 2016， 博士

【摘要】 光纤传感技术是以光波为载体,光纤为媒质,感知和传感外界被测量信号的新型传感技术。作为被测信号载体的光波和作为传播媒质的光纤,具有抗电磁干扰能力强、易为各种光电探测器件接收、方便光电转换以及适用于远程监测等优点。光纤传感技术的发展趋势是高灵敏度、高精度、多参数、同步在线、功能集成以及网络化等。本论文系统研究了包括干涉传感、激光传感、腔衰荡传感和偏振传感四种新型结构的光纤传感器的工作原理。并在分析上述传感器的理论基础上,对它们应用于温度、浓度和旋光角的测量进行了详细的实验探究,主要研究内容及创新成果包括以下几个方面。（1）在依据光纤中模式传播特性基本原理的基础上,对错位光纤、无芯光纤和法拉第旋镜组成的混合马泽-迈克尔逊结构的模式干涉和错位光纤传感结构不同位置处的电场分布进行理论建模分析,并进一步对干涉信号模式传播的数据进行拟合,深入比较和分析了使用法拉第旋镜消除光纤中的偏振态变化、补偿极化引起的信号衰减和消除外部扰动的原因和结果,为光纤混合干涉型传感技术应用于温度和浓度测量研究奠定了基础。（2）对混合马泽-迈克尔逊结构的模式干涉技术应用于温度和浓度测量进行了系统结构合理设置的实验研究。1)灵敏度增强型基于错位光纤的混合马泽-迈克尔逊干涉的温度传感系统。通过使用法拉第旋镜使光纤传感器具有较宽的应用测量范围,同时该系统可以有效地消除偏振状态随机变化带来的影响,提高了系统的灵敏度和稳定性。2)基于无芯光纤的多模干涉效应理论,实现了一个单模-无芯-单模-错位结构的温度自补偿的温度和浓度测量传感系统。所制备的单模-无芯-单模-错位传感部分最后通过检测反射的包层模波长漂移实现了对温度和液体浓度的测量,该系统的稳定性得到进一步提高。同时创新性的实验验证了无芯光纤对三种重金属溶液浓度的线性传感规律,为在一定范围内为检测重金属溶液浓度提供了一种有效的手段。对比分析了基于错位光纤的激光测温方法与FRM干涉测温方法,二者主要不同点在于错位光纤在激光测温系统中相当于滤波器,激光输出位置只选择在错位光纤干涉光谱的波峰处,因此,激光的中心波长将随着温度的变化而发生平移。实验对比结果表明,错位光纤的FRM干涉测温法灵敏度和稳定性均优于激光测温法。实现了对错位光纤温度传感系统和无芯错位光纤浓度传感系统测量数据的光谱分析和算法优化处理。分别利用改进BP神经网络和改进ELMAN神经网络实现了测量系统的数据分析和预测。给出了改进神经网络结构,详细分析了网络训练过程和参数的选取,最后分别对比说明了温度和浓度数据的预测值分析及误差分析,同时验证了该算法在光纤温度和浓度传感上的可行性,这也为错位光纤在压力、曲率等其他物理量传感上的精确测量提供了新思路。（3）提出了基于错位光纤的腔衰荡光谱技术的温度传感系统。根据朗伯-比尔定律理论分析了环腔损耗及衰荡时间与错位传感部分随温度变化的关系,错位量的变化和由温度引起的错位长度的变化最终可以通过测量衰荡时间检测出来,该系统改进了光谱解调方式并简化了信号的采集处理过程。实验结果表明,当选择不同错位量时,通过曲线拟合获得了衰荡时间τ和错位量D之间的关系,错位量对衰荡输出波形有较大的影响。若输入光功率足够大,错位光纤的引入使腔内总损耗增加从而导致衰荡时间明显减少。（4）针对现有干涉型浓度传感系统存在的测量精度不高和解调困难等问题,提出了一种新型两级调制的磁致旋光角和浓度的偏振测量传感系统。这种技术将传统的直流调制磁光检测技术与交流调制磁光检测技术相结合,去除了纯交流调制产生的磁旋光角变化引起的误差。设计实现了脉冲宽度调制控制的交直流调制信号源。实验验证了掺铽(Tb³⁺)光纤可以用于交直流调制旋光溶液浓度测量系统,该系统采用包括对准装置在内的全光纤链路,使传感设备更便携和紧凑。更多还原

【Abstract】 Optical fiber sensing technology is a new detection technology sensing signal,which is based on light wave as carrier,and optical fiber as medium.As the carrier of the measured signal and the medium of communication,the optical fiber has the ability to resist electromagnetic interference,easy to be received by the variety of photoelectric detector,expedient to facilitate the photoelectric conversion,suitable for remote monitoring and so on.The development trend of optical fiber sensing technology is aiming for high sensitivity,high precision,multi-parameter,synchronous online,function integration and network,etc..In this paper,the working principle of fiber optic sensors,which include four kinds of new structures,comprising interference sensor,laser sensor,cavity ring down sensor and polarization sensor are studied systematically.On the basis of analyzing the theory of these sensors,the experimental measurement of temperature,concentration and rotation angle of the sensors are inquired in detail.The main research contents and innovative achievements include the following aspects.（1）Based on the principle of mode propagation according to the characteristics of the fiber,electric field distribution of the Mach-Zehnder interference and Michelson interference mixed structure is analysized.Mixed structure corresponding to the mode interference optical fiber sensor structure is composed of dislocation optical fiber,no core fiber and Faraday rotation mirror.The theoretical model of dislocation at different positions is building,and the interference signal transmission mode data is further to fit.The method of the using Faraday rotation mirror to eliminate the polarization state changes,to compensate polarization caused by fiber signal attenuation and to eliminate the effect of external disturbance is in-depth compared and analysized.The study for hybrid fiber interferometric sensing technology applied to the temperature and concentration measurement is significant and indispensable.（2）The experimental study on the mixed structure of mode interference technology is applied to the temperature and concentration measurement.1)Temperature sensing system based on the mixed structure interferometer with enhanced sensitivity.With the application of using Faraday rotation mirror,the optical fiber sensor has been possessed a wide measurement range and characteristic to effectively eliminate the influence of random polarization state changes.Finally,the sensitivity and the stability are improved.2)based on the multimode interference effect theory of the no core fiber,a temperature self compensating sensing system including temperature and concentration measurement is realized.The measurement of temperature and liquid concentration by detecting the wavelength shift of the reflected cladding mode is realized by using the single-mode/no-core/Single-mode/dislocation sensing part,and the stability of the system is further improved.At the same time,the linear feature of the concentration sensing about the three kinds of heavy metal solution is verified by the experimental results,which providing an effective means to detect the concentration of heavy metal solution in a certain range.The temperature measurement method based on the dislocation optical fiber between laser sensing and FRM interferometer are analyzed and compared.The main difference between the two methods are that the dislocation fiber is equal to the filter in the laser temperature measurement system.The position of the laser output is only selected at the wave crest of the interference spectrum.Therefore,the center wavelength of the laser will shift with the change of temperature.The experimental results show that the sensitivity and the stability of the FRM interference sensing method are better than that of the laser temperature sensing method.The dates of spectral analysis and algorithm optimization measured by the dislocation optical fiber temperature sensing system and the no core dislocation fiber concentration sensing system are achieved.By using the improved BP neural network and the improved ELMAN neural network,the expected and predicted results of the sensing system are realized.An improved neural network architecture is presented.The process of network training and the selection of parameters are analyzed in detail.Finally,the forecast value and error of temperature and concentration data are compared and analyzed.At the same time,the feasibility of the algorithm is verified in the optical fiber temperature and concentration sensing.It is also provides a new idea for the accurate measurement of the pressure,curvature and other physical quantities of the misplaced optical fiber.（3）The temperature sensing system based on the fiber cavity ring down spectroscopy technology is proposed.According to the Lambert-Beer Law theory,the ring cavity loss and the relation between the ring down time and the dislocation length of sensing part varied with temperature have been analyzed.The variation of the displacement and the change of the offset length caused by the temperature can be detected by measuring the ring-down time.The method of spectrum demodulation is improved and the process of signal acquisition and processing is also simplified.The experimental results show that when choosing different displacement,the relationship between the ring-down time and offset D is obtained by curve fitting.Meanwhile,the waveform of ring-down output is affected by the offset.If the input optical power is large enough,the total loss of the cavity is increased,and the ring-down time of the cavity is reduced obviously.（4）In view of the problems of the low precision in measurement and the difficulty to demodulation existing in interferometric concentration sensing system,a new type of two-stage modulation of the optical rotation angle and the concentration of the polarization measurement sensor system is proposed.This technology combines the traditional DC-modulation magneto-optic detection technology with the AC-modulation magneto-optic detection technology.The error brought by the change of the magnetic rotation angle is caused by the method of pure AC modulation.The AC/DC modulation signal source with pulse width modulation control is designed and implemented.It is experimental verified that the terbium-doped(Tb³⁺)optical fiber can be used for AC/DC modulation concentration measurement system.The system adopts an all optical fiber link including the alignment device,which makes the sensing equipment more portable and compact.更多还原